As a conventional wireless communication system, there is a wireless LAN system that is standardized by the IEEE 802.11 (See non-patent references 1 and 2).
A technology in which transmission is controlled according to priority of data has been known in the field of the wireless LAN technology. Patent reference 1 discloses a technology in which a coding rate and a modulation method are controlled according to priority of packets. In addition, patent reference 2 discloses a technology in which image data is transferred in the above-stated method. The standard of the TGe (IEEE 802.11 Task Group e) for specific priority is described in non-patent reference 3 shown below, for example.
On the other hand, in the wireless LAN technology, a MIMO (Multiple-Input Multiple-Output) transmission system is attracting a lot of attention. The feature of the MIMO transmission lies in the arrangement that enables, in a wireless transceiver, higher transmission speed than that of conventional wireless LAN systems and stable communication even under multi-path (reflected wave) environment by performing data transmission and reception by using a plurality of antennas for subsequent data synthesis and decoding.
Known examples of the MIMO transmission include a method as shown in non-patent reference 4 in which original transmit data is divided into a plurality of transmission streams, which are then transmitted simultaneously from a plurality of antennas (SDM: Space Division Multiplexing), and a method as shown in non-patent reference 5 in which, while using the same data rate as the case where an antenna is used for each of regular transmission and reception, wireless transmission is performed more securely than conventional methods by using transmission/reception diversity (STBC: Space Time Block Coding). The MIMO signal processing under the SDM method makes it possible to set the data rate higher in proportion to the number of transmission antennas unlike a wireless system where an antenna is used for each of regular transmission and reception. While it will not make the data rate higher, the signal processing under the STBC method realizes more assured wireless transmission with the increased number of antennas.
It should be noted that patent reference 3 shown below discloses a wireless communication system of a hybrid type where a transmission method according to the MIMO standard and a transmission method based on another standard are combined.
[Patent Reference 1]
Japanese Patent Laid-open No. 2004-179821
[Patent Reference 2]
Japanese Patent Laid-open No. 2003-134077
[Patent Reference 3]
Japanese Patent Laid-open No. 2004-515176
[Non-patent Reference 1]
IEEE Std. 802.11a-1999, IEEE
[Non-patent Reference 2]
IEEE Std. 802.11g-2003, IEEE
[Non-patent Reference 3]
Edited by Masahiro Morikura, Shuji Kubota, “Revised 802.11 High-Speed Wireless LAN Text Book”, Dec. 21, 2004, Impress
[Non-patent Reference 4]
P. W. Wolniansky, G. J. Foschini, G. D. Golden, R. A. Valenzuela, “V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-Scattering Wireless Channel”, Proc. IEEE ISSSE-98, Pisa, Italy, Sep. 30, 1998, IEEE
[Non-patent Reference 5]
Vahid Torokh, Siavash M. Alamouti, Patric Poon, “New Detection Schemes for Transmit Diversity with no Channel Estimation”, Proc. IEEE ICUPC1998, pp. 917-920, Vol. 2